Liquid crystal display device with active matrix substrate using source/drain electrode as capacitor conductor

ABSTRACT

A liquid crystal display device has a plurality of gate bus wirings and source bus wirings on one of paired substrates. Moreover, a inter-layer insulating film made of an organic material is provided on thin film transistors of respective picture elements, and a picture element electrode is provided on the inter-layer insulating film. Furthermore, the liquid crystal display device is provided with an additional capacity common wiring which is provided on the inter-layer insulating film and forms an additional capacity section between the picture element electrode and the additional capacity common wiring.

This application is a divisional of prior application Ser. No.08/718,051, filed Sep. 13, 1996, now U.S. Pat. No. 5,917,563.

FIELD OF THE INVENTION

The present invention relates to a liquid crystal display deviceincluding switching elements such as thin film transistors (TFT) on eachpicture element and relates to a manufacturing method thereof.

BACKGROUND OF THE INVENTION

The following describes an arrangement of a conventional liquid crystaldisplay device in which a peripheral driving circuit is formed on one ofpaired substrates on reference to FIGS. 16 through 18.

FIG. 16 is a plan view showing a substrate with which a peripheraldriving circuit is formed, and FIG. 17 is a drawing showing a layout ofone picture element. Moreover, FIG. 18 is a cross-sectional view takenalong line 18--18 in FIG. 17.

As shown in FIG. 16, a gate driving circuit 32, a source driving circuit33 and a TFT array section 34 are formed on an insulating substrate 31which is one of the substrates in the liquid crystal display device. Asthe insulating substrate 31, a glass substrate, a quartz substrate orthe like is used. The gate driving circuit 32 is composed of a shiftregister 32a and a buffer 32b. Moreover, the source driving circuit 33is composed of a shift register 33a, a buffer 33b and analog switches39. The analog switches 39 sample video signals to be inputted from theoutside to a video line 38.

A plurality of parallel gate bus wirings 116 which are extended from thegate driving circuit 32 are wired on the TFT array section 34. Moreover,a plurality of parallel source bus wirings 120 extend from the sourcedriving circuit 33 wired on the TFT array section 34 so as toperpendicularly intersect to the gate bus wirings 116. The analogswitches 39 are connected respectively to the source bus wirings 120.Moreover, additional capacity common wirings 114 are wired on the TFTarray section 34 so as to be parallel with the gate bus wirings 116.Rectangular domains which are surrounded respectively by two gate buswirings 116, two source bus wirings 120 and two additional capacitycommon wirings 114 are provided with thin film transistors (i.e. TFT)35, picture elements 36 and additional capacities 37. The TFT 35functions as a switching element which electrically connects the pictureelement 36, the gate bus wiring 116 and the source bus wiring 120. Agate electrode of the TFT 35 is connected to the gate bus wiring 116,and a source electrode of the TFT 35 is connected to the source buswiring 120.

A drain electrode of the TFT 35 is connected to a picture elementelectrode of the picture element 36. The picture element 36 is composedof the picture element electrode, a counter electrode provided on acounter substrate which faces the insulating substrate 31, and a liquidcrystal layer sealed between the picture element electrode and thecounter electrode. Moreover, the additional capacity common wiring 114is connected to a electrode having the same electric potential as thecounter electrode.

The following details the arrangement of the conventional TFT arraysection 34 in FIG. 16 with reference to FIGS. 17 and 18. A polycrystalsilicon thin film 111 which is used as an active layer of the TFT 35 isformed on the insulating substrate 31 so as to have a thickness of, forexample, 40 nm-80 nm. Then, a gate insulating film 113 is formed so asto have a thickness of, for example, 80 nm-150 nm by the sputtering orCVD method.

Phosphorus ions (P⁻) with concentration of 1×10¹⁵ (cm⁻²) are implantedinto a section 110 (a shaded portion in FIGS. 17 and 18) of thepolycrystal silicon thin film 111 where the additional capacity 37 willbe formed.

A metal or polycrystal silicon layer with low resistance which is usedas the gate bus wiring 116 and the additional capacity common wiring 114are formed on the gate insulating film 113, and it is patterned so as tohave a predetermined shape. As a result, a gate electrode 116a and anadditional capacity upper electrode 114a are formed.

Thereafter, in order to determine a conduction type of the TFT 35,phosphorus ions (P⁺) with concentration of 1×10¹⁵ (cm⁻²) are implantedfrom the upper section of a gate electrode 116a, and a portion under thegate electrode 116a of the polycrystal silicon thin film 111 is achannel section 112 of the TFT 35.

A first inter-layer insulating film 115 is formed on the whole surfaceof the substrate 31 by using SiO₂ or SiN_(X), and contact holes 118 and119 are provided. Then, the source bus wiring 120 and a piling electrode(drain electrode) 121 are formed in the contact holes 118 and 119 byusing metal with low resistance such as Al.

In the same manner as the first inter-layer insulating film 115, asecond inter-layer insulating film 124 is formed on the whole surface ofthe substrate 31 by using SiO₂ or SiN_(X), and a contact hole 123 isformed. Then, a picture element electrode 125 is formed by using atransparent conductive film such as ITO. When Al is used for the sourcebus wiring 120 and the piling electrode 121, for example, in order tobring the piling electrode 121 into ohmic contact with the pictureelement electrode 125, a barrier metal 126 is formed in the contact hole123 by using metal such as Ti, TiW, Mo, MoSi.

However, the above-mentioned conventional liquid crystal display devicehas the following problems.

(1) First Problem

In the above arrangement, since the first and second inter-layerinsulating films 115 and 124 are made of inorganic materials, the filmthickness is small, i.e. several hundred nm, and the dielectric constantbecomes higher than a usual organic material. For this reason, thecapacity between the additional capacity common wiring 114 and the otherwiring (for example, the source bus wiring 120) becomes large, and theadditional capacity common wiring 114 is easily influenced by the otherwirings. Therefore, when inorganic materials are used for theinter-layer insulating films 115 and 124, it is not preferable that theadditional capacity section is formed so as to greatly overlap the otherwirings.

In addition, when the picture element electrode 125 is arranged so as tooverlap the gate bus wiring 116 or the TFT 35 on an area connected tothe picture element 36, capacity Cgd' is generated between the pictureelement electrode 125 and the gate bus wiring 116 or the TFT 35. Whenthe TFT 35 is turned off, a voltage drop (ΔV) of the picture elementelectrode 125 represented by the following equation occurs.

    ΔV=ΔVg×(Cgd+Cgd')/(Cgd+Cgd'+Cs+C.sub.LC)

(ΔVg: potential difference between on-state and off-state of the gate,Cgd: capacity between gate and drain of TFT, Cs: additional capacity,C_(LC) : liquid crystal capacity)

Since a d.c. component is applied to the liquid crystal due to thevoltage drop, it is required to apply a bias voltage, for example, tothe counter electrode.

In addition, since the additional capacity section does not have a lighttransmitting characteristic, an aperture ratio is lowered due to theadditional capacity section. Moreover, the additional capacity commonwiring 114 is formed on the layer where the gate bus wiring 116 isformed, and the additional capacity common wiring 114 does not have thelight transmitting characteristic. As a result, the aperture ratio islowered.

(2) Second Problem

Since the first inter-layer insulating film 115 is made of a inorganicmaterial with a thickness of several hundred nm, disconnection of thesource bus wiring 120 occurs due to unevenness of surface in a sectionwhere the source bus wiring 120 and the gate bus wiring 116 cross eachother.

(3) Third Problem

In the above arrangement, the additional capacity common wiring 114 isformed by using the same material as the gate bus wiring 116, and thegate insulating film 113 just under the wiring 114 is used as adielectric. Since the gate insulating film 113 is thin and itsdielectric constant is high, even if the area is small, large additionalcapacity can be obtained. However, with this arrangement, when the gatebus wiring 116 is formed by a material with electrically higherresistance than the source bus wiring 120, propagation of a signal tendsto be delayed in the additional capacity common wiring 114.

(4) Fourth Problem

In the liquid crystal display device having the above arrangement, apoint-at-a time driving method is generally executed. As the otherdriving method, a line-at-a-time driving method exists, when theline-at-a-time driving is executed, a sampling capacitor for holding asampled signal for 1 line is required. Moreover, since it is necessaryto apply a transfer signal to be used for outputting the signals storedin the sampling capacitor to a hold capacitor all at once, theconfiguration of the circuit becomes complicated. The point-at-a-timedriving does not require these capacitors, and thus a simpleconfiguration of the circuit can be realized. Furthermore, thepoint-at-a-time driving method is usually used. However, thepoint-at-a-time driving method requires a higher speed of writing to thepicture element through the TFT 35 compared to the line-at-a-timedriving method. For this reason, when a-SiTFT is used as the TFT 35, thepoint-at-a-time driving is not executed, but when p-SiTFT is used, itcan be executed.

In the point-at-a-time driving, video signals inputted to video lines 38shown in FIG. 16 are successively sampled by the analog switches 39 ofthe source driving circuit 33 so as to be written to the source buswirings 120. Thereafter, when the TFT 35 is turned on according to asignal from the gate driving circuit 32, the video signal written to thesource bus wiring 120 is written to the picture element 36. Therefore,electric charges corresponding to the video signals written to therespective source bus wirings 120 should be securely held at least untilthe writing to all the source bus wirings 120 is completed.

When the capacity of the source bus wiring 120 is small, since an amountof electric charges written through the analog switches 39 is small, thewriting to the picture element 36 is insufficient. As a result,insufficient contrast occurs. More specifically, when a inter-layerinsulating film having a low dielectric constant and a large thicknessis used, also the capacity formed in a portion where the source buswiring 120 and another wiring cross each other becomes small. As aresult, the capacity of the source bus wiring 120 becomes less and less.

As a method of preventing the insufficient contrast due to aninsufficient capacity of the source bus wiring 120, for example,Japanese Unexamined Patent Publication No. 62-178296/1987 (Tokukaisho62-178296) suggests that a sample hold capacity is formed by an MOS-typecapacitor having the same structure as the TFT 35. However, such anMOS-type capacitor is liable to cause a dielectric breakdown due tostatic electricity during the rubbing treatment which is given to analignment film on a side where the TFT 35 is provided after the processof manufacturing a substrate. Since the dielectric breakdown of theMOS-type capacitor causes a defect of line because a suitable signalcannot be written to the picture element which is connected to thesource bus wiring 120 which is provided with this MOS-type capacitor.

As described in Japanese Unexamined Patent Publication No. 7-175082/1995(Tokukaihei 7-175082), for example, such a defect of line can becorrected by forming a plurality of sample hold capacity parallel and bycutting off a defective capacity when the dielectric breakdown occurs.However, in this case, a new process for correcting the defect is added.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide a liquidcrystal display device having high aperture ratio which does not causelowering of the aperture ratio due to an additional capacity (commonwiring).

Moreover, it is a second object of the present invention to preventdisconnection of a source bus wiring which is a conventional problem.

Furthermore, it is a third object of the present invention to provide aliquid crystal display device having high aperture ratio without aproblem of delayed propagation of a signal in the additional capacitycommon wiring and a method of manufacturing the liquid crystal displaydevice.

In addition, it is a fourth object of the present invention to provide aliquid crystal display device which includes a capacity having anarrangement without no defects in the source bus wiring, holdingsufficient electric charges by means of the capacity and performingwriting to picture elements.

In order to achieve the above objects, a liquid crystal display deviceof the present invention has:

a plurality of scanning lines provided on one of paired substrates;

a plurality of signal lines provided on the substrate so that the signallines cross the scanning lines;

switching elements provided respectively to cross sections of thescanning lines and the signal lines;

a inter-layer insulating film made of an organic material provided onthe switching elements;

a picture element electrode provided on the inter-layer insulating film;and

an additional capacity common wiring for forming an additional capacitysection between the picture element electrode and the additionalcapacity common wiring, the additional capacity common wire beingprovided on said inter-layer insulating film.

In accordance with the above arrangement, the capacity between anadditional capacity common wiring and the scanning lines or the signallines can be ignored, and the additional capacity common wiring can beformed in a desired shape. For example, the additional capacity commonwiring can be used as a light shielding film.

In the above arrangement, it is preferable that the above additionalcapacity common wiring is provided at least in a position where itoverlaps the switching element. With this arrangement, the apertureratio is hardly lowered due to the additional capacity common wiring.Moreover, in this case, it is desired that the additional capacitycommon wiring covers at least a PN junction in the switching element andfunctions as a light shielding film. As a result, the light directed tothe liquid crystal display device 7 is not projected onto the switchingelement, thereby preventing lowering of display quality due to anincrease in OFF-state currents.

Moreover, in the above arrangement, it is preferable that the additionalcapacity common wiring is provided at least in a position where itoverlaps one of the scanning line and the signal line. With thisarrangement, the lowering of the aperture ratio due to the additionalcapacity common wiring hardly occurs.

In addition, in the above arrangement, it is preferable that theadditional capacity common wiring is made of a metal for bringing thedrain electrode of the switching element into ohmic contact with thepicture element electrode. When the additional capacity common wiring isformed by a metal for bringing the drain electrode into ohmic contactwith the picture element electrode, the additional capacity lowerelectrode and the additional capacity common wiring as well as the metalcan be simultaneously patterned. Therefore, an additional process forpatterning the additional capacity lower electrode and the additionalcapacity common electrode is not required.

In addition, in the above arrangement, it is preferable that a countersubstrate which is the other substrate of the paired substrates does nothave a black matrix. Namely, in accordance with the arrangement that thecounter substrate does not have a black matrix, it is not necessary toform a light shielding pattern in enough large size for its marginrequired for the lamination with the counter substrate. Therefore, theaperture ratio can be increased. Moreover, since only a transparentconductive film for switching a liquid crystal material is formed or thetransparent conductive film and a color filter are formed on the countersubstrate, the process for manufacturing the counter substrate becomessimple.

In addition, in the above arrangement, it is preferable that thedielectric constant of the insulating film used as a dielectric of theadditional capacity is larger than the dielectric constant of theorganic material used as the inter-layer insulating film. As a result,the additional capacity can be effectively formed in a small area.

It is preferable that an anodic oxide film is used as the dielectric ofthe additional capacity. Since the anodic oxide film has an excellentcoating characteristic with respect to the additional capacity lowerelectrode and the additional capacity common wiring, the short-circuitof the additional capacity lower electrode and the additional capacitycommon wiring with the picture element electrode does not occur.Moreover, the process of forming an inorganic film by using thesputtering or CVD method is not required.

In addition, in order to achieve the above object, the liquid crystaldisplay device of the present invention has:

a non-monocrystal silicon thin film, a gate insulating film and a gatebus wiring provided on one of paired substrates in this order;

a first inter-layer insulating film made of an organic material beinglaminated on the gate bus wiring; and

a source bus wiring, a second inter-layer insulating film and a pictureelement electrode being provided on the first inter-layer insulatingfilm in this order.

In accordance with the above arrangement, since the first inter-layerinsulating film is made of an organic material, a short-circuit betweenthe gate bus wiring and the source bus wiring through the inter-layerinsulating film generated when the inorganic material is used does notoccur. Moreover, since the surface on which the source bus wiring isprovided can be sufficiently made flat, the disconnection of the sourcebus wiring due to unevenness over the thin film transistor or the gatebus wiring can be prevented. Moreover, the capacity in the positionwhere the gate bus wiring crosses the source bus wiring becomes smaller,thereby suppressing the delay of a signal generated in the bus wirings.

In the above arrangement, it is preferable that the second inter-layerinsulating film is also made of an organic material. As a result, anelectric field to be applied to the liquid crystal layer from the domainbelow the second inter-layer insulating film can be decreased.

Moreover, since the picture element electrode can be formed on thesufficiently flat surface, the rubbing process can be surely performed,thereby eliminating disorder of the alignment of liquid crystal.

In addition, it is preferable that the organic material is aphotosensitive acrylic resin. When the photosensitive acrylic resin isused as the organic material, the contact hole can be easily formed bythe exposing and developing processes, thereby simplifying themanufacturing process. Moreover, since the photosensitive acrylic resinhas an excellent light transmitting characteristic, even when the liquidcrystal display device is used as a transmission-type liquid crystaldisplay device, the transmittance factor is not lowered.

In addition, in the above arrangement, it is preferable that theadditional capacity is formed on the inner wall of at least one contacthole which goes through the first inter-layer insulating film. As aresult, the non-light-transmitting domain due to the additional capacitycan be small, thereby improving the aperture ratio of the liquid crystaldisplay device.

In addition, it is preferable that a piling electrode is formed on theinner wall of the contact hole on which the above additional capacity isformed, and the piling electrode is used as a lower electrode of theadditional capacity. As a result, the lower electrode of the additionalcapacity as well as the source bus wiring can be formed simultaneously,so it is not necessary to specially pattern the lower electrode of theadditional capacity.

Furthermore, in the above arrangement, it is preferable that a lightshielding film is formed on the first inter-layer insulating film. As aresult, it is not necessary to form a light shielding film on thecounter substrate, thereby further simplifying the manufacturingprocess. It is more preferable that the light shielding film is formedby the upper electrode of the additional capacity.

In addition, in order to achieve the above object, the liquid crystaldisplay device of the present invention has:

a non-monocrystal silicon thin film, a gate insulating film and a gatebus wiring being provided in this order on one of paired substrates;

a first inter-layer insulating film, a source bus wiring, a secondinter-layer insulating film and a picture element electrode beingprovided in this order on the gate bus wiring;

an additional capacity composed of an additional capacity upperelectrode and an additional capacity lower electrode, the additionalcapacity upper electrode covering a contact hole provided on the firstinter-layer insulating film and being made of the same material as thesource bus wiring, the additional capacity lower electrode being made ofthe non-monocrystal silicon thin film.

In accordance with the above arrangement, since the additional capacityupper electrode is made of the same material as the source bus wiring,the resistance of the upper electrode is low, thereby arising noproblems of the delayed propagation of a signal on the additionalcapacity upper electrode. Moreover, since the gate insulating film canbe used as the dielectric of the additional capacity, the area of theadditional capacity section as a light shielding film can be reduced.

In the above arrangement, it is preferable that the first inter-layerinsulating film is formed by an organic material. As a result, thesurface on which the source bus wiring is provided sufficiently flat,thereby preventing the disconnection of the source bus wiring due tounevenness over the thin film transistor or the gate bus wiring.

In addition, it is preferable that the organic material hasphotosensitivity. As a result, the contact hole can be formed on thefirst inter-layer insulating film only by the exposing and developingprocesses, thereby, simplifying the manufacturing process.

In addition, a method of manufacturing the liquid crystal display devicehaving the above arrangement has:

the first step of forming the additional capacity lower electrode byusing the non-monocrystal silicon; and

the second step of forming the additional capacity upper electrode byusing the same material as the source bus wiring so that the additionalcapacity upper electrode covers a contact hole provided on the firstinter-layer insulating film.

In accordance with the above mentioned, the delayed propagation ofsignals on the addition capacity common electrode can be eliminatedwithout adding a new device or process to the method of manufacturing aconventional liquid crystal display device. Moreover, since the gateinsulating film is used as the dielectric of the additional capacity, anarea of the additional capacity section as a light shielding film can bereduced, thereby improving the aperture ratio of a liquid crystal panel.

In addition, when the method of forming the first inter-layer insulatingfilm by using a photosensitive organic material, the contact hole can beformed on the first inter-layer insulating film by an optical method,i.e. a simple manufacturing process without the etching process. As aresult, damage to the gate insulating film due to the etching processdoes not occur.

In addition, in order to achieve the above object, the liquid crystaldisplay device of the present invention has:

a pair of substrates;

a liquid crystal layer sandwiched between the pair of substrates;

a display section composed of a plurality of picture elements;

a plurality of picture element electrodes provided respectively on theplurality of picture elements on one of the paired substrates;

a plurality of gate bus wirings and a plurality of source bus wiringsfor driving the plurality of picture elements;

an inter-layer insulating film which covers the gate bus wirings and thesource bus wirings;

switching elements provided in intersections of the gate bus wirings andthe source bus wirings; and

a covered electrode provided on a portion of the source bus wiringoutside the display section, the covered electrode being connected tothe source bus wiring through a contact hole of the inter-layerinsulating film.

In accordance with the above arrangement, the contact hole is providedon the inter-layer insulating film on the source bus wiring locatedoutside the display section, and the covered electrode is formed so asto cover the position of the source bus wiring. For this reason, whenthe pair of substrates are laminated, the disconnection of the sourcebus wiring in the section to which a sealing resin was applied can beprevented.

It is preferable that a counter electrode facing the covered electrodeand the picture element electrode is formed on the other substrate, andthe covered electrode, the counter electrode and the liquid crystallayer form a capacity for holding electric charges written to the sourcebus wiring. In other words, when the capacity is formed by the coveredelectrode, the liquid crystal material and the counter electrode, it isnot necessary to form the capacity by specially utilizing the gateinsulating film. Therefore, a defect in the lines due to anelectrostatic breakage does not occur.

In addition, since the capacity of the source bus wiring can be larger,even if point sequential driving is performed, a decrease in an amountof the electric charges written from the analog switch can be prevented.Therefore, insufficient contrast, which is caused by insufficientwriting of electric charges to picture elements, does not occur.

The covered electrode can be formed by the same material as the pictureelement electrode. Moreover, it is preferable that the covered electrodehas a wider width than the source bus wiring.

In addition, the manufacturing process can be simplified by using aphotosensitive acrylic resin as the inter-layer insulating film.

For fuller understanding of the nature and advantages of the invention,reference should be made to the ensuing detailed description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing which shows a layout of one picture element in aliquid crystal display device according to one embodiment of the presentinvention.

FIG. 2 is a cross-sectional view taken along line 2--2 in FIG. 1.

FIG. 3 is a drawing which shows a layout of one picture element in aliquid crystal display device according to another embodiment of thepresent invention.

FIG. 4 is a drawing which shows a layout of one picture element in aliquid crystal display device according to still another embodiment ofthe present invention.

FIG. 5 is a cross-sectional view of picture elements in a liquid crystaldisplay device according to still another embodiment of the presentinvention.

FIG. 6 is a drawing which shows a layout of one picture element in aliquid crystal display device according to still another embodiment ofthe present invention.

FIG. 7 is a cross-sectional view taken along line 7--7 in FIG. 6.

FIG. 8 is a drawing which shows a layout of one picture element in aliquid crystal display device according to still another embodiment ofthe present invention.

FIG. 9 is a cross-sectional view taken along line 9--9 in FIG. 8.

FIG. 10 is a drawing which shows a layout of one picture element in aliquid crystal display device according to still another embodiment ofthe present invention.

FIG. 11 is a cross-sectional view taken along line 11--11 in FIG. 10.

FIGS. 12(a) through 12(g) are cross sectional view which show steps of amethod of manufacturing the above liquid crystal display device.

FIG. 13 is a drawing which schematically shows an arrangement of aliquid crystal display device according to still another embodiment ofthe present invention.

FIG. 14 is a cross-sectional view taken along line 14--14 in FIG. 13.

FIG. 15 is a cross-sectional view which schematically shows anarrangement of TFT and an additional capacity in each picture element ofthe above liquid crystal display device.

FIG. 16 is an explanatory drawing which shows an arrangement of aconventional liquid crystal display device in which a peripheral drivingcircuit is formed on one of the paired substrate.

FIG. 17 is a drawing which shows a layout of one picture element in theabove liquid crystal display device.

FIG. 18 is a cross-sectional view taken along line 18--18 in FIG. 17.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

The following describes one embodiment of the present invention onreference to FIGS. 1 and 2.

FIG. 1 is a drawing which shows a layout of one picture element in theliquid crystal display device of the present embodiment, and FIG. 2 is across-sectional view taken along line 2--2 in FIG. 1.

The liquid crystal display device of the present embodiment has a pairof substrates like the arrangement of a conventional liquid crystaldisplay device shown in FIG. 16. Moreover, a gate driving circuit, asource driving circuit and a TFT array section are formed on aninsulating substrate 10 which is one of the substrates. A lot ofparallel gate bus wirings (scanning lines) 16 which are connected to thegate driving circuit are provided to the TFT array section. Moreover, alot of parallel source bus wirings (signal lines) 20 which are connectedto the source driving circuit are provided to the TFT array section soas to intersect perpendicularly to the gate bus wirings 16.

Furthermore, an additional capacity common wiring 26A is provided to theTFT array section of the liquid crystal display device so as to beparallel with the gate bus wiring 16.

In addition, in the liquid crystal display device, like the conventionalarrangement, a rectangular domain which is surrounded by the two gatebus wirings 16, the two source bus wirings 20 and the additionalcapacity common wiring 26A is provided with a thin film transistor (i.e.TFT), a picture element and an additional capacity. The TFT functions asa switching element which electrically connects the picture element, thegate bus wiring 16 and the source bus wiring 20. A gate electrode 16a ofthe TFT is connected to the gate bus wiring 16, and a source electrode20a of the TFT is connected to the source bus wiring 20.

A drain electrode 21a of the TFT is connected to a picture elementelectrode 25 of the picture element through a barrier metal 26. Thepicture element is composed of a picture element electrode 25, a counterelectrode provided on a counter substrate which faces the insulatingsubstrate 10, and a liquid crystal layer which is sealed between thepicture element electrode 25 and the counter electrode. Moreover, theadditional capacity common wiring 26A is connected to an electrodehaving the same electric potential as the counter electrode.

As shown in FIG. 2, the additional capacity common wiring 26A is formedon a second inter-layer insulating film 24 made of an organic material.Then, an additional capacity is formed by the additional capacity commonwiring 26A and an insulating film 27 and the picture element electrode25.

The following explains an example of a manufacturing method of theliquid crystal display device according to the present embodiment.

Similarly to the conventional example, a polycrystal silicon thin film11 which becomes an active layer is formed on the insulating substrate10 so as to have a thickness of 40 nm-80 nm. Then, a gate insulatingfilm 13 is formed by using SiO₂ or SiN_(X) by the sputtering or CVDmethod so as to have a thickness of 80 nm. The gate electrode 16a isformed together with the gate bus wiring 16 by using Al or polycrystalsilicon.

Thereafter, in order to determine a conduction type of the TFT,phosphorus ions with concentration of 1×10¹⁵ (cm⁻²) are implanted fromthe upper side of the gate electrode 16a using the gate electrode 16a asa mask. As a result, a non-doped channel section 12 is formed under gateelectrode 16a in the active layer, and domains other than the channelsection 12 are made high-concentration impurity domains. The activelayer of TFT can be arranged so that less leakage currents flow when theTFT is OFF state by providing low-concentration impurity domains ornon-doped domains near the channel section 12.

Next, after a first inter-layer insulating film 15 was formed on thewhole surface, contact holes 18 and 19 were provided. Then, the sourceelectrode 20a and the drain electrode 21a were formed together with thesource bus wiring 20 by using a metal having low resistance such as Al.

In the present embodiment, a transparent photosensitive organic film wasformed by the spin coating method as the second inter-layer insulatingfilm 24. When the second inter-layer insulating film 24 isphotosensitive, the contact holes can be provided only by the exposingand developing processes, thereby simplifying the manufacturing process.

In addition, in the present embodiment, since a liquid crystal panel isused as a transmission-type liquid crystal display device, not a coloredorganic material but a transparent acrylic resin was used as a materialof the second inter-layer insulating film 24. Since the dielectricconstant of this organic film is small, i.e. not more than 4, and thefilm thickness is not less than 2 μm, liquid crystal is not influencedby an electric field from the part below the insulating film. For thisreason, a reverse tilt of the liquid crystal material can be suppressed,and thus an angle of visibility of the liquid crystal panel can be alsomade large. Next, a contact hole 23 was provided by the exposing anddeveloping processes.

The barrier metal 26, for bringing the drain electrode 21a into an ohmiccontact with the picture element electrode 25 to be formed by ITO in thelater step, was formed by metals such as TiW, Ti, Mo and MoSi. In thepresent embodiment, an additional capacity lower electrode, for formingthe additional capacity between the picture element electrode 25 and theadditional capacity lower electrode, and the additional capacity commonwiring 26A were formed by using the metal so as to have a shape shown bya shaded portion in FIG. 1. A metal different from the barrier metal 26may be used as the additional capacity lower electrode and theadditional capacity common wiring 26A.

Next, the insulating film 27 was formed on the additional capacity lowerelectrode and the additional capacity common wiring 26A so that theadditional capacity were formed. The insulating film 27 can be formed bythe anodic oxidation method as long as the barrier metal 26 is made ofan anodically oxidizable material such as Al or Ta. Since the anodicoxide film has larger dielectric constant than an ordinary inorganicfilm, the additional capacity can be effectively formed in a small area.Moreover, since the anodic oxide film has an excellent coatingcharacteristic with respect to the additional capacity lower electrodeand the additional capacity common wiring 26A, a short-circuit of theadditional capacity lower electrode and the picture element electrode aswell as a short-circuit of the additional capacity common wiring 26A andthe picture element electrode do not occur. Moreover, a process forforming an inorganic film by the sputtering or CVD method is notrequired. In order to form the additional capacity effectively, it isdesirable that the insulating film 27 is made of a material having alarger dielectric constant than the second inter-layer insulating film24, a material having a small film thickness or a material having alarge dielectric constant and a small film thickness. More specifically,the satisfactory dielectric constant is not less than 5, and not lessthan 8 is desirable. It is desirable that the film thickness of theadditional capacity section is not more than 500 nm.

As shown in FIG. 1, the picture element electrode 25 was formed on thebarrier metal 26, the additional capacity lower electrode and theadditional capacity common wiring 26A so as to partially overlap thegate bus wiring 16 and the source bus wiring 20. As mentioned above,since the additional capacity is formed on the thick inter-layerinsulating film 24, the additional capacity common wiring 26A can beformed in a desired position. As shown in FIG. 1, in the presentembodiment, since the additional capacity is formed on the TFT, loweringof the aperture ratio due to the additional capacity does not occur.Moreover, since the adjacent picture elements are separated from eachother on the wiring 26A, the wiring 26A functions as a light shieldingfilm. Further, the non-light transmitting additional capacity lowerelectrode exists over the TFT, and since this electrode functions as alight shielding film, thereby making it possible to prevent theproduction of the leakage currents due to the projection of a light to aPN junction of the thin film transistor. In the present embodiment,since the light shielding film is formed on the substrate 10 on whichthe TFT is provided, it is not necessary to form a light shieldingpattern on the counter substrate. As a result, a pattern of atransparent conductive film to be the counter electrode may be formed.Therefore, unlike the case where the light shielding pattern is formedon the counter substrate, it is not necessary to form the lightshielding film so as to be enough large for a laminating margin, therebymaking it possible to increase the aperture ratio.

Embodiment 2

The following describes another embodiment of the present invention inreference to FIGS. 3 and 4. Here, for convenience of explanation, thosemembers that have the same arrangement and functions, and that aredescribed in the aforementioned embodiment 1 are indicated by the samereference numerals and the description thereof is omitted.

In a liquid crystal display device of the present embodiment, theadditional capacity is formed on the bus wiring 16 or 20.

In the present embodiment, the manufacturing process up to the step offorming the second inter-layer insulating film 24 by using the organicfilm made of an acrylic resin or the like is the same as theembodiment 1. As to the organic film, since the dielectric constant issmall and the film thickness is thick, i.e. not less than 2 μm, acapacity between the picture element electrode 25 and the bus wiring 16or 20 can be ignored. Therefore, there arises no problem even if thepicture element electrode 25 is formed over the gate bus wiring 16. As aresult, as shown in FIG. 3, when the picture element electrode 25overlaps the gate bus wiring 16 in the same stage as the electrode 25and when the additional capacity lower electrode and the additionalcapacity common wiring 26A are formed over the gate bus wiring 16, theadditional capacity can be formed over the gate bus wiring 16 and theTFT. In this case, since the additional capacity is formed not only overthe TFT but also over the gate bus wiring 16, the domain for theadditional capacity can be large.

Similarly, the picture element electrode 25 can be formed over thesource bus wiring 20. Therefore, as shown in FIG. 4, the picture elementelectrode 25 overlaps the source bus wiring 20 in the same stage as theelectrode 25, and the additional capacity lower electrode and theadditional capacity common wiring 26A are formed over the source buswiring 20 so that the additional capacity can be formed over the sourcebus wiring 20 and the TFT. In this case, since the additional capacityis formed not only over the TFT but also over the source bus wiring 20,the domain of the additional capacity can be large.

Embodiment 3

The following describes still another embodiment of the presentinvention in reference to FIG. 5. Here, for convenience of explanation,those members that have the same arrangement and functions, and that aredescribed in the aforementioned embodiments are indicated by the samereference numerals and the description thereof is omitted.

In embodiment 1, as shown in FIG. 2, the additional capacity lowerelectrode and the additional capacity common wiring 26A are formedbefore forming the picture element electrode 25. On the contrary, in thepresent embodiment, as shown in FIG. 5, the insulating film 27 and anadditional capacity electrode 28 which is one electrode of theadditional capacity are provided on the picture element electrode 25.Namely, after forming the picture element electrode 25, the insulatingfilm 27 and the additional capacity electrode 28 are formed.

The following explains a manufacturing method of the present embodimentwith reference to FIG. 5.

First, similarly to embodiment 1, after forming the TFT on theinsulating substrate 10, the second inter-layer insulating film 24 wasformed by using an organic material, and the contact hole 23 wasprovided.

Then, only the barrier metal 26 was formed and the picture elementelectrode 25 was formed thereon.

Thereafter, the insulating film 27 was formed, and a metal which is amaterial of the additional capacity electrode 28 was formed thereon soas to cover the whole surface of the substrate. The metal was patterned,and the additional capacity electrode 28 was formed over the TFTsimilarly to embodiments 1 and 2. Moreover, similarly to embodiment 2,the additional capacity electrode 28 may be formed over the gate buswiring 16 or the source bus wiring 20. Also in the present embodiment,when a material having the large dielectric constant or a materialhaving the small film thickness is used as the insulating film 27, theadditional capacity can be formed in a small area effectively.

If the insulating film 27 is left when additional capacity electrode 28is patterned, the insulating film 27 also functions as a protectivefilm. An arbitrary metal can be used as the additional capacityelectrode 28, so the same material as the gate bus wiring 16, the sourcebus wiring 20 or the picture element electrode 25, for example may beused. Moreover, unlike embodiment 1, it is not necessary to form theinsulating film 27 only on the additional capacity lower electrode andthe additional capacity common wiring 26A, and the insulating film isformed on the picture element electrode 25 so as to cover the wholesurface of the substrate. Therefore, it is not necessary to pattern theinsulating film 27.

Embodiment 4

The following describes still another embodiment of the presentinvention with reference to FIGS. 6 and 7. Here, for convenience ofexplanation, those members that have the same arrangement and functions,and that are described in the aforementioned embodiments are indicatedby the same reference numerals and the description thereof is omitted.

FIG. 6 is a drawing which shows a layout of one picture element in theliquid crystal display device of the present embodiment, and FIG. 7 is across-sectional view taken along line 7--7 in FIG. 6.

In the liquid crystal display device of the present embodiment, thefirst inter-layer insulating film 15 is formed by using a photosensitiveacrylic resin which is an organic material.

In addition, the additional capacity is formed on an inner wall of thecontact hole 19 which goes through the first inter-layer insulatingfilm. Namely, the drain electrode (piling electrode) 21a is provided tothe inner wall of the contact hole 19, and the drain electrode 21a isthe lower electrode of the additional capacity. Moreover, an insulatingfilm 50 and an upper electrode 51a for forming the additional capacityare provided to the contact hole 19.

The following explains a manufacturing method of the liquid crystaldisplay device of the present embodiment.

First, similarly to embodiment 1, the polycrystal silicon thin film 11to be an active layer was formed on the insulating substrate 10 made ofglass, quartz or the like so as to have a thickness of 40 nm-80 nm.Next, the gate insulating film 13 made of SiO₂ or SiN_(X) was formed onthe center portion of the polycrystal silicon thin film 11 by thesputtering or CVD method so as to have a thickness of 80 nm.Furthermore, the gate electrode 16a made of Al or polycrystal siliconwas formed on the gate insulating film 13 so as to have a thickness of30 nm.

Thereafter, phosphorus ions (P⁺) with concentration of 1×10¹⁵ (cm⁻²)were implanted from the upper side of the gate electrode 16a by usingthe gate electrode 16a as a mask so that the conduction type of the TFTis determined. As a result, the non-doped channel section 12 was formedunder the gate electrode 16a in an active layer, and high-concentrationimpurity domains were formed on domains other than the channel section12. At this time, the leakage currents at the time of turning off theTFT can be decreased by providing a low-concentration impurity domain ora non-doped domain to the proximity of the channel section 12 on theactive layer of the TFT.

Next, the first inter-layer insulating film 15 was formed on the wholesurface of the substrate 10 by using a photosensitive acrylic resin bythe spin coating method so as to have a film thickness of 2.5 μm.Thereafter, the contact holes 18 and 19 were formed on the firstinter-layer insulating film 15 by the exposing and developing processes.

Here, since the first inter-layer insulating film 15 of not less than 2μm was laminated, the upper surface of the first inter-layer insulatingfilm 15 can be flat. Moreover, since the photosensitive material wasused as the first inter-layer insulating film 15, the contact holes 18and 19 can be formed only by the exposing and developing processes,thereby simplifying the manufacturing process.

Next, the source electrode 20a and the drain electrode 21a were formedby using a low-resistant metal such as Al so as to respectively coverthe inner wall of the contact holes 18 and 19. At this time, the sourcebus wiring 20 is provided together with the source electrode 20a on thefirst inter-layer insulating film 15. Since the lower surface on whichthe source bus wiring 20 is provided is made flat by the firstinter-layer insulating film 15, disconnection of the source bus wiring20 due to unevenness of the surface does not occur even in the sectionwhere the source bus wiring 20 crosses the gate bus wiring 16. Moreover,when the photosensitive acrylic resin material, which has a smallerdielectric constant than an inorganic material, is used as the firstinter-layer insulating film 15, the film thickness can be made large. Asa result, the capacity in the section where the source bus wiring 20crosses the gate bus wiring 16 can be ignored, thereby preventing thedelay of a signal generated in the bus wiring.

In addition, the drain electrode 21a is formed along the inner wall ofthe contact hole 19, and it functions as a lower electrode for formingthe additional capacity.

Next, the insulating film 50 was formed on the whole surface of thesubstrate 10 by using SiN_(X) or the like so as to have a thickness of50 nm. At this time, the insulating film 50 is also formed along theinner wall of the contact hole 19 like the drain electrode 21a. Theinsulating film 50 functions as an insulating film for forming theadditional capacity.

Then, the upper electrode 51a for forming the additional capacity isformed over the contact hole 19 by using a metal such as Ta or Al, andat the same time an additional capacity common wiring 51 is also formed.At this time, since the film thickness of the first inter-layerinsulating film 15 is thicker than the conventional one, i.e. 2.5 μm, asurface area of the inner wall of the contact hole 19 becomes larger. Asa result, the additional capacity value can take a sufficiently largevalue.

Here, a simple explanation will be given as to the value of theadditional capacity.

If an inner diameter of an additional capacity upper electrode 51a inthe contact hole 19 is, for example, 5 μm, the surface area becomes 5×5(bottom)+5×2.5×4 (side)=75 (μm²). Then, the capacity C_(OX) per unitarea of SiN_(X) of 50 nm is 1.4×10⁻³ (pF/μm²), thereby making itpossible to obtain the additional capacity value of 0.11 pF only in thecontact hole 19. If the additional capacity is formed in a plane shape,the domain of 75 (μm²) is required for the additional capacity. However,since this additional capacity domain does not transmit a light, theaperture ratio is lowered by this domain. In the present embodiment,even if the additional capacity value is not sufficient, the additionalcapacity value can be supplemented by forming the contact hole 19 inlarger size or forming the plane capacity supplementally.

Next, the second inter-layer insulating film 24 was formed on the wholesurface of the substrate 10 by using a photosensitive acrylic resinsimilarly to the first inter-layer insulating film 15. Then, the secondinter-layer insulating film 24 was exposed and developed, and theinsulating film 50 was etched so that the contact hole 23 which goesthrough the second inter-layer insulating film 24 and the insulatingfilm 50 was formed. Moreover, the picture element electrode 25 wasformed by using a transparent conductive film such as ITO so as to coverthe contact hole 23. At this time, when an ohmic characteristic of thecontact between the drain electrode 21a and the picture elementelectrode 25 is required, a barrier metal may be formed on the contacthole 23.

In the present embodiment, since the photosensitive acrylic resin wasused for the second inter-layer insulating film 24, similarly to thefirst inter-layer insulating film 15, an electric field, which isapplied to the liquid crystal layer from the domain below the secondinter-layer insulating film 24, can be ignored. Moreover, since thepicture element electrode 25 is formed on the sufficiently plane domain,the secure rubbing process can be performed. Therefore, disorder of thealignment of liquid crystal does not occur.

Embodiment 5

The following describes still another embodiment of the presentinvention with reference to FIGS. 8 and 9. Here, for convenience ofexplanation, those members that have the same arrangement and functions,and that are described in the aforementioned embodiments are indicatedby the same reference numerals and the description thereof is omitted.

FIG. 8 is a drawing which shows a layout of one picture element in theliquid crystal display device of the present embodiment, and FIG. 9 is across-sectional view taken along line 9--9 in FIG. 8.

In the liquid crystal display device of the present embodiment,additional capacity upper electrode 51a is extended above the TFT. Theother arrangement and the manufacturing method are the same asembodiment 4.

In accordance with the above arrangement, since the gate bus wiring 16,the source bus wiring 20 and the additional capacity upper electrode 51afunction as a light shielding film, it is not necessary to form a lightshielding film on the counter substrate. Therefore, the manufacturingprocess can be further simplified.

Embodiment 6

The following describes still another embodiment of the presentinvention with reference to FIGS. 10 to 12. Here, for convenience ofexplanation, those members that have the same arrangement and functions,and that are described in the aforementioned embodiments are indicatedby the same reference numerals and the description thereof is omitted.

FIG. 10 is a drawing which shows a layout of one picture element in theliquid crystal display device according to the present embodiment, andFIG. 11 is a cross-sectional view taken along line 11--11 in FIG. 10.

As shown in FIGS. 10 and 11, the polycrystal silicon thin film 11 isprovided on the insulating substrate 10, and the gate insulating film 13is provided on the polycrystal silicon thin film 11. The gate electrode16a made of Al or polycrystal silicon is provided on the gate insulatingfilm 13. The non-doped channel section 12 is provided under the gateelectrode 16a, and domains other than the channel section 12 are madehigh-concentration impurity domains. Moreover, the first inter-layerinsulating film 15 is provided so as to cover them, and the contactholes 18 and 19 are formed on the first inter-layer insulating film 15.The source electrode 20a and the drain electrode (piling electrode) 21aare electrically connected to the polycrystal silicon thin film 11through the contact holes 18 and 19. Moreover, an additional capacityupper electrode 54 is provided on the inner wall of a contact hole 53formed on the first inter-layer insulating film 15.

In addition, the second inter-layer insulating film 24 is provided onthe first inter-layer insulating film 15, and a contact hole 23 isprovided on the second inter-layer insulating film 24. The pictureelement electrode 25 is connected to the drain electrode 21a through thecontact hole 23. In order to bring the drain electrode 21a into ohmiccontact with the picture element electrode 25, a barrier metal 26 may beformed by using TiW, etc.

The following explains the method of manufacturing the liquid crystaldisplay device having the above arrangement.

FIGS. 12(a) through 12(g) are cross-sectional views which show the stepsof the method of manufacturing the liquid crystal display device havingthe above arrangement.

As shown in FIG. 12(a), the polycrystal silicon thin film 11 as anactive layer was formed on the insulating substrate 10 made of glass orquartz so as to have a thickness of 40 nm-80 nm. Next, the gateinsulating film 13 made of SiO₂ or SiN_(X) was formed on the polycrystalsilicon thin film 11 by the sputtering or CVD method so as to have athickness of 80 nm.

In addition, as shown in FIG. 12(b), the gate electrode 16a made of Alor polycrystal silicon was formed on the gate insulating film 13.Thereafter, P⁺ with concentration of 1×10¹⁵ (cm⁻²) were implanted fromthe upper side of the gate electrode 16a by using the gate electrode 16aas a mask so that the conduction type of the TFT is determined. As aresult, the non-doped channel section 12 was formed under the gateelectrode 16a in an active layer, and high-concentration impuritydomains were formed on domains other than the channel section 12.

If the additional capacity upper electrode 54 was formed by using thesame material as the gate electrode 16a, the ion implantation into anadditional capacity lower electrode domain as well as the forming of thechannel section 12 could not be carried out simultaneously. However, inthe present embodiment, the channel section 12 is formed and at the sametime the resistance of the additional capacity lower electrode can belowered by the ion implantation. Moreover, the active layer of the TFTmay be arranged so that leakage currents in the OFF period of TFT aredecreased by providing the low-concentration impurity domain or thenon-doped domain to the vicinity of the channel section 12.

Thereafter, contact domains 55 and 56 were formed on the gate insulatingfilm 13 on which the contact holes 18 and 19 will be formed later.

Next, as shown in FIG. 12(c), the first inter-layer insulating film 15was formed on the whole surface of the substrate 10 by the spin-coatingmethod by using a photosensitive acrylic resin so as to have a thicknessof 2.5 μm. Here, the upper surface of the first inter-layer insulatingfilm 15 can be made flat by laminating the first inter-layer insulatingfilm 15 so as to have a thickness of not less than 2 μm.

Thereafter, as shown in FIG. 12(d), the contact holes 18 and 19 wereformed on the first inter-layer insulating film 15 by the exposing anddeveloping processes. Moreover, at this time, the contact hole 53 whichbecomes an additional capacity forming section was formed. Since thephotosensitive material was used as the first inter-layer insulatingfilm 15, the contact holes 18, 19 and 53 can be formed only by theexposing and developing processes without the etching process, therebysimplifying the manufacturing process. Since the etching process is notperformed, the gate insulating film 13 thereunder is not damaged,thereby improving reliability.

Next, as shown in FIG. 12(e), the source electrode 20a, the drainelectrode 21a and the additional capacity upper electrode 54 were formedby using metals such as Al having low resistance. The additionalcapacity upper electrode 54 was formed so as to cover the inner wall ofthe contact hole 53.

In addition, the source bus wiring 20 (see FIG. 10) as well as theseelectrodes was formed. At this time, since the lower surface on whichthe source bus wiring 20 is provided is made flat by the firstinter-layer insulating film 15, disconnection of the source bus wiring20 due to unevenness of the surface does not occur even in the crosssection 57 (see FIG. 10) where the source bus wiring 20 crosses the gatebus wiring 16.

In addition, the photosensitive organic resin material used as the firstinter-layer insulating film 15 has smaller dielectric constant than aninorganic material, and its film thickness can be made larger. As aresult, a capacity on the cross section 57 where the source bus wiring20 crosses the gate bus wiring 16 can be ignored, thereby preventingdelayed propagation of signals in the bus wiring. Moreover, since Alhaving low resistance is used as the additional capacity upper electrode54 and an additional capacity common wiring 54A, the delayed propagationof signals in the additional capacity common wiring 54A does not occur.Moreover, since the additional capacity is formed such that the gateinsulating film 13 just under the additional capacity upper electrode 54is used as a dielectric, the aperture ratio is not lowered.

Next, as shown in FIG. 12(f), the second inter-layer insulating film 24was formed by using the photosensitive acrylic resin similarly to thefirst inter-layer insulating film 15. Moreover, as shown in FIG. 12(g),the second inter-layer insulating film 24 was exposed and developed sothat the contact hole 23 was formed, and the picture element electrode25 as a transparent conductive film was formed by using ITO. Ifsatisfactory ohmic contact between the drain electrode 21a and thepicture element electrode 25 cannot be obtained, the barrier metal 26may be formed on the contact hole 23.

As mentioned above, in the liquid crystal display device of the presentembodiment and its manufacturing method, the delayed propagation ofsignals does not occur in the additional capacity common wiring 54A.Moreover, a higher aperture ratio can be realized by using the gateinsulating film 13 as a dielectric of the additional capacity.

Embodiment 7

The following describes still another embodiment of the presentinvention in reference to FIGS. 13 and 15. Here, for convenience ofexplanation, those members that have the same arrangement and functions,and that are described in the aforementioned embodiments are indicatedby the same reference numerals and the description thereof is omitted.

FIG. 13 is a drawing which schematically shows an arrangement of theliquid crystal display device of the present embodiment, and FIG. 14 isa cross-sectional view taken along line 14--14 in FIG. 13. Moreover,FIG. 15 is a cross-sectional view which schematically shows arrangementsof the TFT and the additional capacity in each picture element.

As shown in FIG. 13, the liquid crystal display device of the presentembodiment has the insulating substrate (TFT substrate) 10 and a countersubstrate 58. A display section 62 in which a plurality of pictureelements are arranged in a matrix pattern is provided on the TFTsubstrate 10, and a gate driving circuit 63 and a source driving circuit64 for driving the picture elements are formed around the displaysection. The gate bus wiring 16 is extended from the gate drivingcircuit 63 into the display section 62, and the source bus wiring 20 isextended from the source driving circuit 64 into the display section 62.The gate bus wiring 16 and the source bus wiring 20 are arranged so asto intersect perpendicularly to each other. Moreover, the additionalcapacity common wiring, not shown, is provided on the display section 62so as to be parallel with the gate bus wiring 16.

The TFT substrate 10 and the counter substrate 58 are laminated eachother by a sealing resin 59, and a liquid crystal material is sealedtherebetween so that a liquid crystal layer 60 (see FIG. 14) is formed.When voltages are selectively applied to the liquid crystal layer 60 bythe counter electrode 61 formed on the counter substrate 58 and thepicture element electrode on each picture element, display is carriedout.

The following describes an example of the method of manufacturing theliquid crystal display device according to the present embodiment.

First, the polycrystal silicon thin film 11 which becomes an activelayer is formed on the TFT substrate 10 so as to have a thickness of 40nm-80 nm, and the gate insulating film 13 is formed thereon by thesputtering or CVD method. SiO₂ film or SiN_(X) film can be used as thegate insulating film 13. In the present embodiment, a glass substrate isused as the TFT substrate 10, and the polycrystal silicon thin film 11is formed thereon so as to have a thickness of 50 nm. Then, the SiO₂film is formed by the CVD method so as to have a thickness of 80 nm.Then, phosphorus ions are implanted into a portion where the additionalcapacity will be formed later (shaded portion in FIG. 15), namely, aportion under an additional capacity common wiring 65 so that theresistance becomes low.

Thereafter, an Al film or polycrystal silicon film is formed as the gatebus wiring 16 and the additional capacity common wiring 65 so as to bepatterned in a desired shape. At this time, the gate insulating film 13is patterned simultaneously. The gate bus wiring 16 has a protrudingsection because of the patterning, and this protruding section is usedas the gate electrode 16a of the TFT shown in FIG. 15. In the presentembodiment, the Al film was formed by the sputtering method so as tohave a thickness of 300 nm. After the patterning, phosphorus ions areimplanted into the polycrystal silicon thin film 11 from the upper sideof the gate electrode 16a by using the gate electrode 16a as a mask sothat the conduction type of the TFT is determined. As a result, thenon-doped channel domain 12 is formed in the polycrystal silicon thinfilm 11, and domains in the polycrystal silicon thin film 11 other thanthe channel domain 12 are made a high-concentration impurity domains. Inthe present embodiment, the phosphorus ions having concentration of1×10¹⁵ (cm⁻²) was implanted. Here, the active layer 11 may be arrangedso that leakage currents are decreased by providing thelow-concentration impurity domain or the non-doped domain to thevicinity of the channel domain 12.

Next, the first inter-layer insulating film 15 is formed on the wholesurface of the TFT substrate 10, and the contact holes 18 and 19 areprovided thereto. It is preferable that the thickness of the inter-layerinsulating film 15 is not less than 2 μm. In this case, it is possiblethat the inter-layer insulating film 15 has a flat surface which is notinfluenced by the existence/non-existence and a shape of each componentspositioned under the inter-layer insulating film 15. In the presentembodiment, a photosensitive acrylic resin was used as the firstinter-layer insulating film 15, and this resin having a thickness of 2.5μm was applied to the TFT substrate 10 by the spin-coating method sothat the contact holes 18 and 19 were formed by the exposing anddeveloping processes. Since the photosensitive insulating material isused, the contact holes can be formed only by the exposing anddeveloping processes, thereby simplifying the manufacturing process.

Next, low-resistant metal films such as Al, which are used as the sourceelectrode 20a and the drain electrode (piling electrode) 21a, areformed, and the low-resistant metal films are patterned in a desiredshape so that the source electrode 20a and the drain electrode 21a areobtained. Moreover, the source bus wiring 20 as well as these aboveelectrodes are simultaneously formed. In the present embodiment, the Alfilm was formed so as to have a thickness of 300 nm.

Then, the second inter-layer insulating film 24 is formed on the wholesurface of the TFT substrate 10, and the contact hole 23 is providedthereto. Moreover, the transparent conductive film is formed thereon,and it is patterned in a desired shape so that the picture elementelectrode 25 is formed. In the present embodiment, similarly to thefirst inter-layer insulating film 15, the photosensitive acrylic resinwas used as the inter-layer insulating film 24, and this resin wasapplied to the TFT substrate 10 by the spin-coating method so as to havea thickness of 2.5 μm. Thereafter, the contact hole 23 was formed by theexposing and developing processes. Moreover, an ITO film having athickness of 150 nm was used as the picture element electrode 25. In thecase where satisfactory ohmic contact of the drain electrode 21a withthe picture element electrode 25 cannot be obtained, a barrier metal maybe formed in the contact hole 23. As mentioned above, a display section62 is formed on the TFT substrate.

In the present embodiment, the thick organic material having smalldielectric constant is used as the inter-layer insulating films 15 and24. For this reason, the capacity of the source bus wiring 20 becomessmall, and this causes insufficient contrast. In order to prevent thisproblem, in the liquid crystal display device of the present embodiment,the capacity is provided to the source bus wiring 20 by utilizing thesource bus wiring 20 between the display section 62 and the sourcedriving circuit 64. The following describes the arrangement of a sectionbetween the display section 62 and the source driving circuit 64 in theliquid crystal display device of the present embodiment on reference toFIG. 14.

As shown in FIG. 14, in the section between the display section 62 andthe source driving circuit 64, the source bus wiring 20 is formed on thefirst inter-layer insulating film 15 having a flat surface, and thesecond inter-layer insulating film 24 is formed on the source bus wiring20 so as to cover the whole surface of the TFT substrate 10. The contacthole 23 for connecting the drain of the TFT and the picture elementelectrode 25 is formed in the section of the inter-layer insulating film24 in the display section 62 as mentioned above, but in the sectionbetween display section 62 and the source driving circuit 64, as shownin FIG. 14, contact holes 66 are formed on the respective source buswirings 20. In the present embodiment, since the photosensitive acrylicresin is used as the inter-layer insulating film 24, the contact holes66 are formed only by the exposing and developing processes.

Next, a covered electrode 67 is formed so as to cover the source buswiring 20 between the display section 62 and the source driving circuit64. In FIG. 13, for simplification of the drawing, only a part of thecovered electrode 67 is shown, but the covered electrode 67 can beprovided on all the source bus wirings 20. The covered electrode 67 isformed simultaneously with the picture element electrode 25 bypatterning a transparent conductive film to be the picture elementelectrode 25. When a width L₂ of the covered electrode 67 is made widerthan a width L₁ of the source bus wiring 20, the capacity can be formedeffectively. In the present embodiment, the width L₁ of the source buswiring 20 was 5 μm and the width L₂ of the covered electrode 67 was 20μm. The covered electrode 67 faces the counter electrode 61 formed onthe counter substrate 58 across the liquid crystal layer 60 so that thecapacity is formed. Electric charges written to the source bus wiring 20are held by the capacity. In the present embodiment, in order to preventthe problem of insufficient contrast, a capacity 2 pF was formed by thecovered electrode 67 and the counter electrode 61. The width L₂ of thecovered electrode 67 is determined so that enough capacity for holdingelectric charges is secured.

As mentioned above, in the liquid crystal display device of the presentembodiment, the capacity for holding the electric charges written tosource bus wiring 20 is formed between the display section 62 on which aplurality of picture elements are arranged and the source drivingcircuit 64. Therefore, even if an inter-layer insulating film havingsmall dielectric constant is used, displaying with sufficient contrastcan be performed.

In addition, in the liquid crystal display device of the presentembodiment, the wiring between the display section 62 and the sourcedriving circuit 64 has a two-layered structure composed of the wiring 20and the covered electrode 67. Disconnection can occur in the section towhich the sealing resin 59 was applied when the TFT substrate 10 and thecounter substrate 58 are laminated to each other. The above two-layeredstructure is successful for preventing the disconnection. In thetwo-layered structure, disconnection of the gate bus wiring 16 can bealso prevented by providing the covered electrode to the sealed portionof the gate bus wiring 16.

In addition, in the liquid crystal display device of the presentembodiment, even if the source bus wiring 20 is in the display section62 or between the display section 62 and the source driving circuit 64,the source bus wiring 20 can be covered with a transparent conductivefilm. In this case, when the picture element electrode 25 and thecovered electrode 67 are formed by etching a transparent conductivefilm, the source bus wiring 20 is not damaged by etchants, therebypreventing the disconnection of the source bus wiring 20 at the time ofetching the transparent conductive film.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A liquid crystal display device comprising:anon-monocrystal silicon thin film, a gate insulating film, and a gatebus wiring provided on one of paired substrates in this order:a firstinter-layer insulating film made of an organic material laminated abovesaid gate bus wiring; and a source bus wiring, a second inter-layerinsulating film, and a picture element electrode provided above saidfirst inter-layer insulating film in this order.
 2. The liquid crystaldisplay device according to claim 1, wherein the organic material is aphotosensitive acrylic resin.
 3. The liquid crystal display deviceaccording to claim 1, wherein an additional capacity for holdingelectric charges of said picture element electrode is formed on an innerwall of at least one contact hole which goes through said firstinter-layer insulating film.
 4. The liquid crystal display deviceaccording to claim 3, wherein a piling electrode is provided forelectrically connecting the non-monocrystal silicon thin layer and thepicture element electrode, the piling electrode extending in a directionof a thickness of the first inter-layer insulating film at the innerwall of the contact hole on which the additional capacity is formed andthe piling electrode being a lower electrode of the additional capacity.5. The liquid crystal display device according to claim 1, wherein alight shielding film is provided above said first inter-layer insulatingfilm.
 6. The liquid crystal display device according to claim 5, whereinthe light shielding film is formed by upper electrode of additionalcapacity.
 7. The liquid crystal display device according to claim 1,wherein said second inter-layer insulating film is made of an organicmaterial.
 8. The liquid crystal display device according to claim 7,wherein the organic material is a photosensitive acrylic resin.
 9. Theliquid crystal display device according to claim 7, wherein anadditional capacity for holding electric charges of said picture elementelectrode is formed on an inner wall of at least one contact hole whichgoes through said first inter-layer insulating film.
 10. The liquidcrystal display device according to claim 9, wherein a piling electrodeis provided for electrically connecting the non-monocrystal silicon thinlayer and the picture element electrode, the piling electrode extendingin a direction of a thickness of the first inter-layer insulating filmat the inner wall of the contact hole on which the additional capacityis formed and the piling electrode being a lower electrode of theadditional capacity.
 11. The liquid crystal display device according toclaim 7, wherein a light shielding film is provided above said firstinter-layer insulating film.
 12. The liquid crystal display deviceaccording to claim 11, wherein the light shading film is formed by anupper electrode of an additional capacity for holding electric chargesof said picture element electrode.
 13. A liquid crystal display device,comprising:a thin film transistor including a semiconductor layer, agate insulating layer, and a gate electrode; a first inter-layerinsulating film provided above the thin film transistor; a sourceelectrode and a piling electrode provided above the first inter-layerinsulating film; a second inter-layer insulating film provided above thepiling electrode; a picture element electrode provided above the secondinter-layer insulating film; and an additional capacity for holdingelectrode charges of the picture element electrode provided between thefirst and second inter-layer insulating films; wherein the pilingelectrode electrically connects the semiconductor layer and the pictureelement electrode and the piling electrode extends in a direction of athickness of said first inter-layer film, and wherein the additionalcapacity includes a first electrode and a second electrode, the firstelectrode is the piling electrode, and at least one of the first andsecond inter-layer insulating films is made of an organic material. 14.The liquid crystal display device according to claim 13, wherein aninorganic insulating film is formed between the second electrode and thepiling electrode.
 15. The liquid crystal display device according toclaim 14, wherein the inorganic insulating film is a silicon nitridefilm.
 16. The liquid crystal display device according to claim 13,wherein the additional capacity is formed on an inner wall of a contacthole formed on the first inter-layer insulating film.
 17. A liquidcrystal display device, comprising:a thin film transistor including asemiconductor layer, a gate insulating layer, and a gate electrode; afirst inter-layer insulating film provided above the thin filmtransistor; a source electrode and a piling electrode provided above thefirst inter-layer insulating film; a second inter-layer insulating filmprovided above the piling electrode; a picture element electrodeprovided above the second inter-layer insulating film; and an additionalcapacity for holding electrode charges of the picture element electrodeprovided between the first and second inter-layer insulating films;wherein the piling electrode electrically connects the semiconductorlayer of the thin film transistor and the picture element electrode andthe piling electrode extends in a direction of a thickness of said firstinter-layer film, and wherein the additional capacity includes a firstelectrode, a second electrode, and an inorganic insulating film providedbetween the first and second electrodes, the first electrode is thepiling electrode, and the inorganic insulating film has a greaterdielectric constant than at least one of the first and secondinter-layer insulating films.
 18. The liquid crystal display deviceaccording to claim 17, wherein the inorganic insulating film is asilicon nitride film.
 19. The liquid crystal display device according toclaim 17, wherein the additional capacity is formed on an inner wall ofa contact hole formed on the first inter-layer insulating film.
 20. Aliquid crystal display device, comprising:a thin film transistorincluding a semiconductor layer, a gate insulating layer and a gateelectrode; a first inter-layer insulating film provided above the thinfilm transistor; a second inter-layer insulating film provided abovesaid first inter-layer insulating film; a picture element electrodeprovided above said second inter-layer insulating film; a drain/sourceelectrode connecting a drain/source region formed in said semiconductorlayer of said thin film transistor to said picture element electrode,said drain/source electrode comprising a conductive material lining afirst opening formed in said first inter-layer insulating film; anotherelectrode insulated from said drain/source electrode by an electrodeinsulating film, said second electrode comprising conductive material insaid first opening that is insulated by said insulating film from theconductive material lining the first opening; and a source/drainelectrode connecting a source/drain region formed in said semiconductorlayer of said thin film transistor to a source/drain line formed abovesaid first inter-layer insulating film and below said second inter-layerinsulating film, wherein said drain/source electrode, said electrodeinsulating film and said other electrode constitute an additionalcapacity for storing electric charges of said picture element electrode.21. The liquid crystal display device according to claim 20, whereinsaid picture element electrode is connected to said drain/sourceelectrode via an opening formed in said second inter-layer insulatingfilm.
 22. The liquid crystal display device according to claim 20,wherein said first inter-layer insulating film comprises an organicmaterial.
 23. The liquid crystal display device according to claim 22,wherein the organic material is a photosensitive acrylic material. 24.The liquid crystal display device according to claim 20, wherein saidother electrode further comprises conductive material extending abovesaid thin film transistor.
 25. The liquid crystal display deviceaccording to claim 20, wherein said other electrode is connected to anadditional capacity common wiring layer.
 26. The liquid crystal displaydevice according to claim 20, wherein the thickness of said firstinter-layer insulating film is not less than 2 micrometers.
 27. Theliquid crystal display device according to claim 20, wherein saidadditional capacity is at least 0.11 pF.